The present disclosure relates to variable cycle gas turbine engines, and more particularly to a three-stream engine architectures.
Gas turbine engines, such as those which power modern military aircraft, include a compressor section to pressurize a supply of air, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases and generate thrust. Downstream of the turbine section, an augmentor section, or “afterburner”, is operable to selectively increase the thrust. The increase in thrust is produced when fuel is injected into the core exhaust gases downstream of the turbine section and burned with the oxygen contained therein to generate a second combustion.
Variable cycle gas turbine engines power aircraft over a range of operating conditions yet achieve countervailing objectives such as high specific thrust and low fuel consumption. The variable cycle gas turbine engine essentially alters a bypass ratio during flight to match requirements. This facilitates efficient performance over a broad range of altitudes and flight conditions to generate high thrust for high-energy maneuvers yet optimize fuel efficiency for cruise and loiter.
Variable cycle gas turbine engines are typically of a three-stream engine architecture in which a two-stage fan directly feeds all three streams, e.g., core stream, second stream, third stream. Typically, a part-span booster fan stage feeds the core stream and the second stream. Although effective, this architecture may challenge hot section design due to the limited area available to execute three streams in the same required package space of traditional two stream engines.